The present invention relates to a thread supplying device for intermittent thread consumption.
Known thread supplying devices of this type are disclosed for example in the patent documents DE35 06 552 A1, ES-PS 9 500 543, DE 94 00 778 U1. These devices in particular in knitting machines are used during intermittent thread consumption either to supply a thread with a smallest possible thread tensioning to a machine which consumes the thread or to interrupt the thread supply. This is needed for example in round knitting machines with: stripers, with which several threads with different properties, for example colors, can be treated on one knitting location. A correspondingly selected thread is therefore supplied and introduced into the knitting needles of the knitting machine, while all other threads of the same stripers are held outside of the knitting region and not introduced into the knitting needles. The exchange of a directly supplied thread to another thread which is to be supplied later is performed in a known manner, for example as disclosed for example in the German patent document DE 195 11 949 A1, by means of turnable thread guide fingers as well as cutting and clamping elements and does not have to be explained for a person skilled in the art. Alternatively, the above described thread supplying devices can be used for example in cases in which only a single thread must be supplied or not supplied to a corresponding knitting system in accordance with a pattern.
In order to guarantee a good thread transportation during the thread supplying phases, the thread supplying drums in the known thread supplying devices are provided with two peripheral portions alternatingly acting to the threads to be supplied, which portions are separated from one another in the axial direction in the thread drum and provided for the possibility to bring the threads along a relatively great peripheral angle in contact with the friction surfaces of the supply drum. In contrast, for performing a fast exchange between supplying and not supplying or visa versa a control lever is provided with two guiding elements, through which the threads which abut in a supply position of the control lever along the relatively great peripheral angle on both peripheral portions, in a non supplying position of the control lever alternatingly act only along a relatively small peripheral portion with the thread drum and therefore are not supplied.
Since in fast running round knitting machines the transition between maximum thread consumption and thread stoppage or visa versa is performed very fast, the thread supplying device must be also formed so that it reacts fast during a corresponding exchange. For this purpose the control lever as a rule is formed as a spring and arranged so that with stopped thread its non supplying position is assumed. During the beginning of a thread consumption from the side of the round knitting machine and the like, the control lever is then automatically moved against the spring force into its supply position, so that the thread is supplied. In contrast, when the thread consumption ends the control lever under the action of the spring force is automatically moved back into the non supplying position.
Finally, it is known to provide the supplying devices for taking into consideration different thread properties, with further, manually adjustable guiding elements. With these elements, the peripheral angle along which the thread alternatingly cooperates with the two peripheral portions, can be changed. This is disclosed for example in the German patent document DE 35 06 552 A1.
Thread supply devices of this type have several basic disadvantages. For a good thread supply with low thread tension it is for example desirable to provide as good friction surfaces as possible, or in other words surfaces with high friction values or friction coefficients with respect to the utilized threads and to place the threads with a sufficiently great peripheral angle on the peripheral portions. For a fast thread stoppage during transition of the thread supplying device to the non supplying position to the contrary the smallest possible friction values and smallest possible peripheral angle is desired. These both requirements can not be brought optimally in coordination with one another, so that the threads can be supplied either with not sufficiently small tension or during transition to the non supplying position have the tendency to remain glued to the second peripheral portion and not to wind on it until they are torn off. A further disadvantage is that the advantage obtained with the second peripheral portion to provide double grade thread placement surface is at least partially eliminated in that the threads due to the required guiding and conducting elements are deviated many times so much that high friction occurs. Finally, it is disadvantageous that an optimization of the control lever which is advantageous in certain circumstances is reduced due to narrow space conditions and from other structural reasons. Therefore, in the known thread supplying device of the above described type, either no sufficiently small thread tension is obtainable or problems with fast transition from the supplying position to non supplying position due to the described glueing action can be expected. Moreover with respect to the thread tensions and also the glueing properties, a desired dependency on the thread material, such as for example polyester, acetate, takes place, so that frequently special adaptation of the thread material selected for the individual cases is needed.